In an ion implanter, it is general to cause a wafer to scan (translate) in a reciprocating motion in the particular straight direction so that the every portion of the wafer surface can be uniformly implanted by ions.
One of the conventional, general wafer scanning devices which makes a wafer scan in a reciprocating motion is described as follows referring to FIG. 13. FIG. 13 shows the inner structure of the vacuum chamber where a wafer holder and other components are placed. In the device of FIG. 13, a drive shaft 81a is connected to an arm 81 and another arm 82, which are used to cause a wafer holder 85 to linearly reciprocate.
Following are the details of the device. The first arm 81 is hollow and has both a drive shaft 81a and a driven shaft 81b in it. The shafts 81a and 81b are connected with a belt 81c. The second arm 82 has a bar-shape and is connected to the driven shaft 81b at its base portion. When the drive shaft 81a in the first arm 81 is rotated by means of a drive source such as a motor (not illustrated), the driven shaft 81b rotates while revolving together with the first arm 81 to change the position and angle of the second arm 82. The top portion of the second arm 82 is connected to the slide member 83 which moves along the guide member 84. The slide member 83 is fixed with a wafer holder 85. Accordingly the wafer holder 85 can linearly move by the rotation of the drive shaft 81a. 
A similar device is also seen in the disclosure of Japanese publication of unexamined patent application No. H10-326590 (see FIG. 4 in the concerned gazette).